It is shown that large potential variations can exist inside the wake of sounding rockets moving with supersonic velocity through the summertime mesopause region. The potential distribution is driven by charge separation induced by the shock wave of the rocket. The low conductivity conditions due to the attachment of free electrons to aerosol particles allow large electric fields, of the order of V/m, to be maintained. The numerical results from a simple model are consistent with recent electric field measurements carried out by the DROPPS-1 sounding rocket.